Photo: AP

At least 50,000 militants from so-called Islamic State have been killed since the US-led coalition started fighting in Iraq and Syria two years ago, a US military official has said, the BBC reports.

The senior official described the figure as a “conservative estimate”.

The figure showed air power and a small number of US figures supporting local forces were having an impact, the official said.

The US has, however, repeatedly warned that IS can replace fighters rapidly.

The official on Thursday said that coalition air strikes could be intensified in places like Mosul, which Iraqi troops are now battling to recapture, but that had to be offset against the risk of civilian casualties.